1. Field of the Invention
The present invention relates to a method of depositing diamond films having uniform thickness by means of microwave enhanced CVD and a light emitting device formed by this method.
2. Description of the Prior Art
Many attempts have been proposed to deposit diamond films by microwave assisted CVD, since diamond is regarded promissing as a future material for electronic devices. Particularly, diamond light emitting devices have attracted interest of many researchers, because of its high thermal resistance, chemically stabilities and low price suitable for mass production, in view of a great demand for light emitting devices in the market. An example of such devices is described in Japanese Patent Application No. sho 56-146930. It is, however, very difficult to deposit high quality diamond films having uniform thicknesses at high deposition speeds required for production on a commercial base.
The deposition conditions of prior art diamond formation have been such that; the reactive gas is composed of a hydrocarbon diluted by hydrogen at about 1-5%; the pressure of the reactive gas during deposition is about 5-20 Torr; the input power of microwaves is 1-5 KW; and the deposition is carried out in a magnetic field of 2 KG. Crystal surfaces can be observed by a microscope even in the surface of diamond films deposited by such a prior art method. The deposition speed achieved by these deposition methods, however, have been limited up to 667 angstrom thickness per hour, i.e. it takes 15 hours to deposit a one micrometer thick diamond film. Furthermore, the area coated by diamond is limited only to 3 cm.phi. keeping the disparity in thickness within 10%. Still further, the quality of diamond deposited is not so high. Graphite is also deposited and gets mixed into diamond films. The graphite component has been confirmed by Raman spectroscopic anylysis.
It is also known to use carbon monoxide diluted by hydrogen at 1-5%. The pressure in a reaction chamber in this case is 0.1-1 Torr. The deposition speed, however, is also low. It takes more then 10 hours to deposit a diamond film of one micrometer thickness even when input energy is applied at 3-5 KW. The deposited area within which a uniform diamond film can be deposited is only up to 5 cm square. The more problematic disadvantage of this method is etching of inner walls of the chamber. The etching causes metallic contamination in diamond films deposited. The metal is such as Fe constituting the wall. This contamination was confirmed by Auger electron spectroscopy. The etching product is coated also on a window through which microwaves are admitted to the chamber and form an impediment of the microwave introduction.